1. Field of the Invention
The present invention relates to nanotubes, and more particularly, to carbon nanotube-based electronic devices.
2. Background of Invention
Single-walled carbon nanotubes (SWNTs) are nanometer-diameter cylinders consisting of a single graphene sheet wrapped up to form a tube. Nanotubes of varying lengths and diameter can be fabricated. However, a typical SWNT can have a diameter of 2 mm and a length of 100 μm. Depending on how the graphene sheets are rolled, nanotubes can have a number of different structures. FIGS. 1A-C illustrates an armchair structure, zigzag structure and a chiral structure for a nanotube, respectively. Multi-walled carbon nanotubes (MWNT) also exist. These are essentially SWNTs within SWNTs. A variety of methods exist to fabricate carbon nanotubes, including laser evaporation, carbon arc methods and chemical vapor deposition.
Both experiment and theory have shown that SWNTs can be either metals or semiconductors, and that their electrical properties can often exceed the properties of the best metals and semiconductors. The remarkable electrical properties of SWNTs stem from the unusual electronic structure of the two-dimensional (2D) material graphene. Specifically, a SWNT has a bandgap in most directions in k-space, but has a vanishing bandgap along specific directions and is called a zero-bandgap semiconductor. Paul L. McEuen et al., Electron Transport in Single-Walled Carbon Nanotubes, MRS BULLETIN, April 2004 at 272.
SWNTs have extraordinary electrical and mechanical properties that can be leveraged to support a wide range of nanotube-based electronic devices. In particular, SWNTs have higher electrical current density and thermal conductivity that any metal. For example, a copper wire with a cross sectional area of 3×1012 nm2 has a current density of 2 million electrons per nm2-sec, while a SWNT with a cross sectional area of 3 nm2 has a current density of 200 billion electrons per nm2-sec. Furthermore, SWNTs exhibit ballistic electron transport in which there is no backscattering of electrons, which is a source of electrical resistance in metals. In addition to these electrical properties, SWNTs are mechanically stronger than most, if not all other materials.
Numerous potential applications have emerged for nanotubes. Among some of the applications contemplated, nanotubes can be used for field emission and shielding, transistors, fuel cells, chemical sensors and catalytic agents for other chemical processes.
Nanotubes have emerged as a possible solution to the increasing demand for smaller, more capable and more reliable sensors for low cost and adaptable surveillance. In general, advances in electronics are shrinking the size of radios and sensors, such as military handheld radios, biologic and chemical sensors and micro power impulse radar systems, for example. Within these systems conventional sized antennas have the negative characteristic of dominating system volume. Replacing conventional system antennas, however, with small antennas often has an undesirable consequence because small antennas are inefficient. In other devices, smaller switches are needed, and improvements to low loss, high permeability materials are needed to continue to support the increasing demands of miniaturization and energy efficiency required by small electronic devices.
What are needed are small electronic devices made from materials that are efficient, and can meet the growing miniaturization needs of electronic systems.